Why would you not want a way to send out messages to people in a form that anyone can see and only people that are looking for it can know the true message? :P

(i.e. you're being held captive, You are able to use a computer, but all of your communication is being monitored and filtered. How do you go about delivering a message to warn your friends about what has happened?)

A family member works in the police gathering evidence on internet paedophiles. He says that steganography is employed fairly often where one image is hidden within another, since there are freeware tools to do it quite easily.